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Non-controlling Interest (Details) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017
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Noncontrolling Interest [Line Items] |  |
Total non-controlling interests | $ (144.4) | $ (131.7)
Total Non-Controlling Excluding Reciprocals |  |
Noncontrolling Interest [Line Items] |  |
Total non-controlling interests | $ 45.7 | $ 31.5
HG Global |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 3.10% | 3.10%
Total non-controlling interests | $ 14.8 | $ 15.9
NSM Holding Co LLC |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 5.00% | 0.00%
Total non-controlling interests | $ 14.1 | $ 0.0
MediaAlpha |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 37.80% | 35.70%
Total non-controlling interests | $ 15.3 | $ 13.1
Buzzmove |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 22.90% | 22.90%
Total non-controlling interests | $ 1.5 | $ 2.5
Build America Mutual |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 100.00% | 100.00%
Total non-controlling interests | $ (190.1) | $ (163.2)

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